Conventionally, frequency allocation for new services or frequency allocation to new operators has been led by the government. In particular, if new operators are present, new frequencies have been allocated thereto through auction or existing frequencies have been reallocated thereto through retrieval from existing operators, so that restricted frequency resources are distributed.
However, as the demand for radio data traffic has explosively increased due to the spread of various radio Internet based applications such as an open mobile terminal platform, a web store, a mobile voice-over-Internet protocol (VoIP), etc., government-driven frequency allocation is considerably inefficient and it becomes increasingly difficult to ensure new frequencies in a frequency distribution table.
Especially, along with rapid growth of broadcast and communication systems, a next-generation communication system has been designed in the form of convergence of multiple networks, the system has become increasingly complicated, and the necessity of linking the networks to each has been gradually expanded. In addition, as communication technology and services have developed, frequency resources are frequently used and, as a specific frequency band has been fixedly occupied to provide better communication technology and services, frequency depletion has becomes a problem.
Recently, frequency sharing schemes have been proposed as a method for solving such a problem. Thereamong, there is technology for adaptively and opportunistically using a spectrum hole (or white space) which is temporally/spatially unused due to low utilization among frequency bands assigned as unlicensed bands in TV broadcast bands. If a primary user having a license for the used bands is discovered, use of the bands should be immediately stopped or the transmit power of the bands should be adjusted so that the primary user is not harmed. A system for performing frequency sharing using the spectrum hole is referred to as a television band device (TVBD) or a television white space (TVWS) system and networks or devices using a shared frequency resource in the TVBD or TVWS system are referred to as TVBD or TVWS networks or devices.
Meanwhile, regardless of whether a communication session between the TVWS networks or devices in the TVWS system is in a normal state, a TVWS network or device may attempt to perform a specific procedure through message transmission and reception to and from another TVWS network or device. If the communication session is not in a normal state, the above attempt is unnecessary and may lead to waste of a frequency/channel resource or a power resource.